var dataString = "Substring removing"

var start = dataString.index(
    dataString.startIndex, offsetBy: 9)
var end = dataString.endIndex
dataString.removeSubrange(start..<end)
//dataString is "Substring"
print("dataString is \(dataString)")

start = dataString.startIndex
end = dataString.index(
    dataString.startIndex, offsetBy: 2)
dataString.removeSubrange(start...end)
//dataString is "string"
print("dataString is \(dataString)")